 It is not until after the Danish invasions that it becomes easier to draw a distinction between the burhs that served as military strongholds for national defence and the royal vills which served no such purpose.Some of the royal vills eventually entered the class of boroughs, but by another route, and for the present the private stronghold and the royal dwelling may be neglected.It was the public stronghold and the administrative centre of a dependent district which was the source of the main features peculiar to the borough.